Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume 61, Issue 45, Pages 10787-10797Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jf402570e
Keywords
short-chain amylose; waxy maize starch; crystallization; spherulites; digestibility
Funding
- Agricultural Experiment Station [12-102-J]
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A novel process combining enzymatic debranching, melting, and crystallization was developed to produce spherulites from short linear alpha-1,4-linked glucans (short-chain amylose, SCA) with controlled enzyme digestibility. SCA was obtained by completely debranching waxy maize starch at 50 degrees C and 25% solids in 0.01 M sodium acetate buffer. The mixture was then heated to 180 degrees C followed by cooling and crystallization to form well-developed spherulites. Multiple analytical techniques including light microscopy, scanning electron microscopy, differential scanning calorimetry, wide-angle X-ray diffraction, and synchrotron small-angle X-ray scattering (SAXS) covered over S orders of length scale and were applied to study the morphology and structure of the spherulites. Spherulites crystallized at low temperatures (4 and 25 degrees C) had a large size (5-10 pm), a B-type starch X-ray diffraction pattern, a lower melting temperature (70-110 degrees C), and a higher digestibility (Englyst method) compared to the spherulites crystallized at 50 degrees C, which had a small size (1-5 mu m), an A-type diffraction pattern, a higher melting temperature (100-140 degrees C), and a lower digestibility. Intact spherulites along with small fragments were observed after digestion with a mixture of alpha-amyase and amyloglucosidase, indicating that digestion was not homogeneous and preferentially occurred in weak spherulites. A second exposure of the undigested residues to the amylases showed a similar digestive pattern as with the parent spherulites, suggesting that the spherulites were hydrolyzed by enzymes at essentially a constant digestion rate between 20 min and 3 h.
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